Apparatus for shrink-wrapping

ABSTRACT

There is disclosed apparatus for pulling a tubular shrinkable polyethylene envelope down over a palletized load wherein opposed gripping devices pinch the opposite faces of the leading edge portion of a flat tubular wrapping that is fed down in a vertical plane to a predetermined level. These gripping devices then move apart, pulling the tubular sheet open to a four-sided envelope. The gripping devices are carried on vertically movable side frames, one of which is at each side of the machine, and when the gripping devices have spread the leading end of the tube open, the side frames move down in unison, pulling the envelope down around the load to be wrapped. When the edge of the envelope is below the pallet, the gripping devices release it, the side frames are raised to the starting position, and the opposed gripping devices are moved back into opposed sheet-gripping position for the next operation. Each required length of tubular wrapper may be transversely heat-sealed, and each length is severed by a cut-off just rearwardly of the heat seal so that the sealed end of the plastic envelope is centered over the top of the load.

United States Patent I I [22] Filed:

Mucka et a1.

[54] APPARATUS ron' SHRINK-WRAPPING [72] Inventors: .Iohn RQMucka; Willia- 11. Dickinson, both'of McCandless Township,

Allegheny County, Pa.

[73] Assignee: Auburn Engineering he.,-Clairton,

Feb. 2, 1970 [21-] Appl. No.: 7,741-

[52] US. Cl. ..53/l83, 53/187 [51] Int; Cl "I651: 1/02, 1365b 43/30 [58] Field of Search ..53/386, 182, 183, 190,30,

[56] References Cited UNITED STATES PATENTS' v 3,621,638 11/1971 Grocke ..53/386 3,025,649 3/1962 7 Stul'tlman... ..53/l82 X 3,112,586 12/1963 Luetzow ..53/29 3,380,220 4/1968 Jennings et a1.'. ..53/24 3,429,095 2/1969 Huson ..53/24 3,508,375 4/1970 Myers 3,514,920 6/1970 Hoffler et a1. 3,529,401 9/1970 Sartore et al. ..53/390 X [451 Dec. 26,1972

Primary Examiner-Theron E. Condon Assistant Examiner-Horace M, Culver Attorney- Pamela, Utzler &. Welsh There is disclosed apparatus for pulling a tubular shrinkable polyethylene, envelope'down over a palletized load wherein opposed gripping devices pinch the opposite faces of the leading edge portion of a flat tubular wrapping that is fed down in a vertical plane to a predetermined level. These gripping devices then move apart, pulling the tubular sheet open to a four- -'sided envelope. The gripping devices are carried on vertically movable side frames, one of which is at each side of the machine, and when the gripping devices have spread the leading end of the tube open, the side frames move down in unison, pulling the envelope down around the load to be wrapped. When the edge fof the envelope is below the pallet, the gripping devices release it, the side frames are raised to the starting position, and the opposed gripping devices are moved back into opposed sheet-gripping position for the next operation. Each required length of tubular wrapper may be transversely heat-sealed, and each length is severed by a cut-off just rearwardly of the heat seal so that the sealed end of the plastic envelope is centered over the top of the load.

18 Claims, 12 Drawing Figures PATENTED DEC 28 I972 SHEET 1 BF 4 INVENTORS JOHN R. MUCKA and WILL 1.4M h. DICKINSON 1M, 4 7 1.42.4

Mair Attorneys PATENTED DEC 2 6 I972 SHEEI 2 [1F 4 INVENTORS JOHN R.-MUC/(A and WILLIAM H. DICKINSON WM W 44 Meir Attorneys PATENTED M2 M2 3,707,064

SHEET 3 [1F 4 Meir Attorneys APPARATUS FOR SHRINK-WRAPPING FIELD OF THE INVENTION AND BACKGROUND This invention is for an improvement in the shrinkwrapping method and apparatus disclosed in Bitsura, et al application, Ser. No. 750,497, filed Aug. 6, 1968 and assigned to our assignee.

In the Bitsura et al. application there is disclosed a method of and apparatus for enveloping a palletized load of articles or the like in a shrinkable polyethylene wrapper. According to said application, the polyethylene wrapper in the form of a flattened tube is fed from a continuous roll, transversely heat-seamed at 9 regular intervals, guided to the top of a supporting frame, and from about the mid plane of the top of the frame guided down through pinch rolls past a cut-off device arranged to sever each length of tubing just above the heat seam, so that the leading edge of the succeeding length of wrapper can be opened out into a generally square tube. Provision is made in said appli cation for opening such leading edge of the flat tubular wrapper by means of horizontally traveling suction belts moving in opposite directions so that one face of the flattened tube is pulled laterally from the center toward the side in one direction, andthe other face in the other direction. At the limit to which the tube can be opened, opposed vertically arranged downwardly traveling suction belts pull the now opened-out tube down over the palleted load to be wrapped until the lower end of the tube is below the level of the pallet or other load support. At the proper time the next seam will have been severed and the closed end of the envelope will lie across the center of the load, all as fully explained in said application.

A difficulty with this arrangement is that while the suction belts will readily attach themselves to the polyethylene film, they can slide or slip on the film without breaking the suction so that the belts may move without always moving the envelope at the same rate of speed. Lacking any positive non-slip grip, the operation was not as fast or positive as desired, and there wasa chancethat the envelope might not be opened out and pulled down evenly.

BRIEF EXPLANATION OF THE PRESENT INVENTION The present invention utilizes a machine structure formed of structural sections much like that disclosed in the Bitsura, et al application, and the flattened tubular polyethylene shrink wrapping is pulled from a roll near the base of the structure, guided upwardly through means for forming a transverse heat seam at regular intervals, and then guided across the top of the machine to the longitudinal center and fed vertically downward between parallel pinch rolls toward the load to be wrapped, which load is centered on a supporting conveyor means under the descending film.

With the present invention, however, there is a vertically movable side frame structure in each of the two longitudinal sides of the machine structure. Each of these side frames is movable from a raised position where the frames extend above the top of the load to a lowered position where they extend below the load support or conveyor. Each frame has a structure pivotally connected thereto which swings from a horizontal position when the side frame is raised downwardly and outwardly toward the side frame. Each such pivoting structure has spaced sheet-gripping and clamping elements at spaced intervals at the free outer end thereof. When the frames are raised, these arcuately pivoting structures are horizontal with their respective sheet-gripping and clamping elements being opposite each other and close to the plane in which the flat tubular sheet is being lowered.

At the appropriate time, a suction is created in each gripping and clamping element that pulls a portion of the confronting face of the flat tubular sheet into the device where a mechanical clamp then grips it. After one face of the flat tubular sheet has been gripped in this way by the gripping and clamping elements on one side, and the other face gripped by the similar elements on the other side, the arcuately movable structures swing downwardly and outwardly, opening the flat tubular wrapping out into a square or rectangular tube. When the gripping and clamping elements have separated to open the tube as far as it will open, the side frames are moved down in unison to pull the now open end of the wrapper down over the load. When the gripping and clamping elements reach a level below the bottom of the load, the clamps are operated to release the wrapper and the side frames are raised and the arcuately movable structures with their gripping and clamping elements raised to the horizontal position for the next operation.

The tubular wrapper will have been transversely heat-seamed at a predetermined distance back from the leading edge, and there is a cut-off mechanism under the pinch rolls, but above said arcuately movable structures, and as the heat seam reaches this cut-off while the wrapper is being pulled down over the load, the operation will be stopped, and the flat tubular wrapper cut just above the heat seam, so that the wrapped load will have the closed seam extending along the top.

Provision is made for rotating the sheet-gripping and clamping elements in a direction opposite the direction in which the arcuately swinging structure on which they are mounted is swinging, so that said elements always maintain their axes parallel with their original position perpendicular to the vertically descending sheet.

This apparatus provides a machine in which the flat tubular wrapping is gripped, pulled open and pulled down around the load without being released after it is once gripped until the operation is complete and there can be no slipping or relative movement between the shrink-wrap sheet and the gripping and clamping elements during the operation of applying the wrapping around the load.

THE DRAWINGS In the drawings which illustrate a preferred embodiment of the invention:

FIG. 1 is an end elevation of the machine with the progressive movement of the clamps from the starting position to the end of their travel being indicated by dotted lines;

FIG. 2 is a side elevation of the apparatus shown in FIG. 1;

FIG. 3 is a top plan view of the apparatus shown in FIG. 2 with the roller conveyor being omitted and with the intermediate portions of the top pinch rolls being broken away to show-the wrapper clamping arrangement beneath;

FIG. 4 is a top plan view of a single clamping element;

FIG. 5 is an elevation looking into the end of the element shown in FIG. 4;

FIG. 6 is a partial transverse section in the plane of line VI-Vl of FIG. 5;

FIG. 7 is a top plan view of the cut-off apparatus removed from the remainder of the machine;

FIG. 8 is a transverse section through the cut-off mechanism, the view being substantially in the plane of line VIII-VIII of FIG. 7-;

FIG. 9, 10 and 11 are simplified schematic views showing respectively the beginning, an intermediate stage, and the final stage of applying the wrapper to a load on a pallet; and I FIG. 12 is a fragmentary view showing a common way in which tubular shrink-wrapping is flat-folded, the view being on a scale somewhat comparable to the diminutive scale of FIGS. 9 to 11.

DESCRIPTION OF THE PREFERRED EMBODIMENT In said copending application it is explained that shrink-wrap polyethylene film is commonly formed first as a large diameter tubular extrusion of indefinite length, and then slit lengthwise and opened out to form a flat sheet, but that the tubular product is also flattened and put up in rolls so that users requiring a tubu-- lar wrapper can unwind it from the roll and open it out into tubular form. One common way of flattening it is to fold two opposite sides of the original tube in toward the center, in the general manner shown in FIG. 12, forming what is known as gusseted tubing T which, when opened out, will have four generally flat sides. If the infolded sides or gussets meet at the center, the flattened tube may be opened out into'a square, or if they do not substantially meet at the center, the flattened tube will be a rectangle with the flat unfolded faces being the longest sides. The present invention will be described in connection with the use of a gusseted tube wrapper, but without excluding two-ply flat tubing as disclosed in said copending application.

v The apparatus comprises a generally rectangular frame made of structural sections and comprising upright structural corner columns 2 and 3 on one side of the machine, and 4 and 5 on the other. The tops of the columns 2 and 3 areconnected by a longitudinally .extending section 6 and the tops of columns 4 and 5 are connected by a similar section 6. In addition there is a top cross member 7 at one end of the machine extending between columns 2 and 4 and a similar member 7 connecting the tops of uprights 3 and S.

- There is a roller conveyor 10 extending lengthwise through the frame close to the floor level from a point in advance of the entrance between columns 2 and 4 to beyond the exit between columns 3 and 5.

On each side of the machine there is a vertically movable frame that is parallel with the axis of the conveyor, the two frames being similar so that similar reference numerals are applied to corresponding parts of each. One such side frame, designated generally as 11, is perhaps best seen in FIG. 2. It has a vertical guide shoe 12 at each end and slides on and is guided by the respective uprights 2 and 3. There is a connecting l3 connecting the two shoes, and there are diagonal braces 14 extending from the top of each shoe down to the cross bar near the center. At the top of each shoe 12 there is mounted a bearing block 15, and a shaft 16 extends horizontally along the top of the frame 11 with its ends fixed in these bearing blocks.

Rotatably mounted on the shaft 16 is a swinging arm structure comprising two parallel arms 17, a cross-connection 17a parallel with shaft 16, and bearings 17b through which the shaft 16 passes. There is a crank arm 17c extending outwardly from the cross-connection 17a. There is a fluid pressure cylinder and piston unit 18 having the piston rod pivotally connected to this crank at 19, and the cylinder is pivotally anchored to the cross bar 13 at 20. By supplying fluid pressure to the lower end of the cylinder 18, the swinging arm structure may be moved from a normal horizontal position through an arc of to a vertical position, and of course can be returned to this horizontal position when pressure is applied to the opposite end of the cylinder.

Thereis a cross member 22 at the outer ends of the arms 17, this cross member including a shaft 23 passing through bearings in the arms and having sprocket wheels 24 at the ends thereof. There is a sprocket 25 on the fixedshaft 16 in line with each sprocket wheel24, and a chain 26 passes around each pair of sprockets 24-25. With this arrangement, when the swinging arm structure is swung down from the horizontal to the vertical position, the shaft 23 and cross member will turn 90 in the opposite direction, the rotation being at the same rate that the arms swing about the shaft 16.

There is a square tube 27 having arms 28 that mount it on the cross member 22, this tube being parallel with shaft 16. p

On each square tube there are two or more wrappergripping elements, designated generally as 30. Each element has a collar 30a adjustably fixed on the square tube 27 by a set screw 30b. Each element also has a flared hollow body 31 resembling somewhat a small vacuum cleaner nozzle, the wide end of thebody being open across almost its full width, theopening being designated 32, and as best seen in FIG. 5, it is of elongated rectangular shape with the long direction of the opening being horizontal. The narrow end of this nozzle element 31 is rigidly fixed to collar 30a.

There is a nipple 33 on the top of the portion 31 that is connected through flexible tubing (not shown) to a motor-driven suction fan or vacuum pump 34, there being a separate suction fan and motor at each side of the machine. Diametrically opposite the suction nipple 33 there is a small fluid pressure cylinder 35' with a piston (not shown) and there is a clamping block 36 (inside the suction element 31) on the free end of the piston rod. As hereinafter more fully explained, the arrangement is such that when a plastic sheet is moved in front of each nozzle element 31, a portion of the sheet is sucked into it and drawn toward the suction nipple, whereupon the cylinder 35 is energized to move the clamping block 36 toward the end of the nipple and clamp it against the interior wall of the member 31. This is indicated in FIG. 6 where a portion of the tubular wrapper T is shown drawn into the clamping nozzle with the block 36 being shown in full lines in its retracted position, and is shown in dotted lines in wrapper-clamping and gripping position. Only when the clamping block is again retracted to the full-line position will the wrapper sheet be released.

By reason of the elements 30 being adjustably fixed on the square bar 27 by clamping screws 30b, it is possible to adjust the suction clamping elements 31 with their clamps along the square tube 27 for use with flattened tubular wrappers of different widths when required for a different size of load.

The two vertically movable side frames, designated generally as 11, and which comprise the shoes 12 and cross member 13 and the various clamping means just described, are provided with means for moving them up and down in unison. As here shown, each vertical shoe 12 has a sprocket chain 40 attached at 41 to its upper end. This chain passes upward over a sprocket 42 on an upper shaft 43 (see FIG. 2) at one side of the machine, and 43a at the other side of the machine. Each sprocket chain extends in a vertical reach down from its sprocket 42 and around a lower sprocket 44 on a shaft 45 at one side of the machine located under shaft 43, and on the other side of the machine, shaft 45:: under shaft 43a. The sprockets 44 and their respective shafts 45 and 450 are at a level well below the top of the roller conveyor 10. After passing around the lower sprockets 44, the several sprocket chains extend upwardly with their ends dead-ended at 46 on the lower ends of the respective shoes 12. Each chain therefore comprises a substantially continuous loop that includes one of the shoes 12.

As best seen in FIG. 2, there is a reversible motor means 47, which may include a reduction gear, for rotating the lower shaft 45, and thereby operating the sprocket chains 40 on one side of the machine to raise or lower that vertically movable side frame 11 that extends between corner posts 2 and 4. Upper shaft 43 has sprocket wheels 48 at each end thereof (see FIG. 2) and cross chains 49 pass around similar sprocket wheels on shaft 4311 (see FIG. 1) to drive shaft 43a and thereby operate the sprocket chains to move the other vertically movable frame 11 that extends between corner posts 4 and 5 so that both frames 11 move up and down in synchronism and isochronism.

Except as above described, the machine is about the same as that shown in said copending application. Near the base of the machine at one side there are brackets 50 that support a roll 51 comprising a continuous length of flattened tubular polyethylene shrink wrapping. The axis of the roll is parallel with the axis of the roller conveyor that is, the roll extends in a foreand-aft direction. The tubular sheet unwinds from this roll, passes under a guide roll 52 between heat-sealing elements 53 and 54 which are electrically heated, and which are normally spaced far enough from each other to be entirely clear of the sealing elements. However, when fluid pressure cylinder 55 or other operating means is actuated, element 53 moves toward element 54, pinching the then stationary tubular sheet between the elements to form a transverse heat seal.

The tubular wrapper extends upwardly, outside the machine frame, over a guide roll 56 on an adjustable bracket 57. The sheet then extends crosswise over the top of the machine to parallel pinch rolls 58 and 59. Roll 58 is intermittently driven by motor and speed reducer unit 60 through a belt or chain 66. The rolls 58 and 59 extend fore-and-aft of the machine and the bight between them is substantially centered above the longitudinal center of the conveyor.

When the roll 58 is driven, the flattened tubular wrapper is unwound from the roll 51, up over roll 56 and down between rolls 58 and 59, moving down in the mid fore-and-aft vertical plane of the machine. Spaced below the rolls 58 and 59, but above the arms 17 when they are raised to the horizontal position shown in FIG. 1, there is the tube cut-off device, designated generally as 62, and which is shown in said copending application, and which is here shown in FIGS. 7 and 8. It comprises a fixed channel structure extending lengthwise of the machine between top cross members 7 and 7', and there is a confronting channel element 71 carried on pivoted arms 72 so that 71 may move toward and away from channel 70. A third channel 73 carries a fluid pressure cylinder and piston 74 for moving channel 71 toward and away from 70. When channel 71 is in the dotted line position shown in FIG. 8, the tubular sheet being fed down between the pinch rolls 58 and 59 can pass freely between channels 70 and 71, but when the travel of the tubular sheet is stopped, channel 71 may be moved by fluid pressure cylinder 74 to clamp the tubular wrapper sheet between the upper flanges of the channels 70 and 71 and also between the lower flanges of these channels while a short reach of tubing is confined between the two flanges to develop proper tension in this portion of the sheet between the two pairs of flanges. The sheet is flexed slightly from a vertical plane when the movable channel 71 pushes it in this way against the fixed channel.

In the fixed channel there is a slide block with a double-edged cutter 75 that is moved lengthwise of the fixed channel transversely across the taut tubular strip clamped between the two pairs of confronting channel flanges. There are cables attached to opposite ends of the slide block and to opposite ends of a piston 76, also positioned in the fixed channel 70. The piston pulls the slide block and knife alternately in one direction and then the other to make alternate cuts in opposite directions.

OPERATION For purposes of illustration, it may be assumed that the load, designated L, is a cube 48 inches on a side, and that it is on a conventional square wooden pallet P having a wood deck about 1 inch thick. Actually, of course, the load may be of some other size and other shape, and be on a support other than a pallet. The shrink-wrap tubing should be of such dimension that it will open out and pull down over the load easily, but should not clear the load by more than about two inches on a side. Since the load has four sides, each 48 inches, and the wrapper may be 2' inches longer on a side, the perimeter of the tube when opened out should be about 4 X 5.2 inch or 208 inch. Formed in the manner shown in FIG. 12, each of the flat sides is about 52 inches and each infolded gusset, when opened out, will be about the same width.

When the sheet is opened out and pulled down over the load, the bottom edge of the envelope should hang about 3 inch below the pallet. Figuring the height of the load at 48 inch, the deck of the pallet l inch, and 3 inches more, the envelope must be 52 inches one-half of the distance across the top of the load, plus some looseness, the envelope from top to bottom should be around 76 to 80 inches in length.

In the operation of the machine, the steps of which are shown in schematic views 9, 10 and 11, the loaded pallet is placed on the conveyor 10 and brought to a position where it is centered in the machine. Assuming the machine is being started up for the first time, the tubular sheet material T will be unrolled in the manner above indicated, and when, for example, 78 inches have been moved between the sealing bars 53-54, the sheet is stopped, and the sealing bars operated to form a transverse heat seam, as is well understood in the art. Thereafter another seam is formed after each 78 inches passes between the sealing bars. The strip feed is stopped when the open leading edge of the flattened tubular strip has been fed down through the pinch rolls and the cut-off device to a level where it is just below the suction-clamp units 30, which are then in the elevated full-line position with the arms horizontal, as

shown in FIG. 1. There are here shown three of these suction-clamp units 30 on each square bar 27 positioned with the units on one side directly confronting the units on the other, and with only a slight distance between those on one side and those on the other. Two of the units on each bar 27 are at the center and there is one on each bar near the end where the side edge portions of the flat tubular sheet is between opposed units.

When the leading edge of the tubular sheet has just passed the suction-clamp units, the suction cups are activated by valving (not shown) and the confronting faces or layers of the folded tube are sucked into the nozzle elements 31 and the clamping cylinders 35 are energized to move the clamping blocks 36 to the dotted line position shownin FIG. 6 and thereby mechanically grip the tube with each face of the tube being gripped at what will be a comer of a square tube. when it is opened out. it is also gripped at a location between the corners.

As soonas the tube is gripped, the cylinders 18 in the respective side frame 12 swing the arms 17 downwardly and outwardly, pulling the tube down and opening it out. At the same time the suction-clamp elements will be rotated so that they remain always in the same plane,'because the shaft 23 rotates in the opposite direction to the arcuate travel of the arms 17 because of the sprockets 24 and 2 5 and sprocket chains 26. It is important that the gripping devices maintain a constant angle with respect to the plane of the sheet which they grip in order that the flattened tube will be properly opened out but not pulled beyond its proper dimensions, and that the maximum clearance between the sides of the load and interior of the envelope not exceed about 2 inches, since this is about the maximum that the sheet will shrink snugly about the load.

When the arms 17 are swung downwardly and outwardly a full90 from the position shown in FIG. 9 to the position shown in FIG. 10, the motor unit 47 will be operated to start to pull the nowopened end of the envelope down around the load by lowering the two side frames 12 through the endless chains 40 as previously described. As soon as the first heat seal reaches the cut,

the operation is stopped and the closed top end of the the seam is centered alongtlie top of the load and the open end of the wrapper is below the pallet. Then the gripping cylinders 35 operate to return clamps 36 to release the film which has been gripped thereby, the motor 47 reversed to raise the frames 12 to their uppermost limit, and cylinder 18 is energized to raise the swinging arms 17 to the original horizontal position. The severed open end of the wrapper is then fed down between the suction-gripping elements 30 ready to repeat the wrapping of the next load.

From the foregoing, it will be seen that the invention provides in a machine for enveloping a preformed load on a pallet or other support a shrink-wrap film wherein a continuous roll of flat tubular film is fonned into a succession of wrappers of the required length, each cut off as it is used, and the leading edge of the succeeding length is engaged at not less than four separate comer areas by clamping means that positively clamp the film, pull it open and down around the load to be enveloped, and then release it. The arrangement in which the clamping elements swing downwardly and outwardly in an arc to open out the flattened tubular blank is especially effective. The fact that while the clamping elements swing downwardly and outwardly through an are without changing their angular relation with respect to the initial vertical plane of the film is important, pulling the film down parallel with the sides of the load and at a predetermined controlled distance therefrom.

The invention has been particularly described in connection with a wrapper which is in the form of a flat gusseted tube, but it may be employed in connection with a simple flat two-ply tube as also described in said Bitsura, et al. application.

We claim:

1. Apparatus for enveloping a load carried on a pallet or other base member in a shrink-film wrapping comprising:

a. a machine structure having upright structural sections and cross members connecting the tops of the upright sections and having means positioned within said structure on which a load to be wrapped is supported,

. means on said machine structure for feeding a flat tubular plastic shrink film downwardly toward a load positioned on said load-supporting means,

c. side frame members movable vertically in said machine structure between a normal raised position at a level extending above the top of a load on said load-supporting means to a level extending below the bottom of said load, one ofsaid movable side frame members being movable in a plane at one side of a load on said load-supporting means and the other in a plane at the opposite side, and

d. sheet gripping means for gripping and partially opening the lower end of the tubular wrapper and mechanical clamping elements on each of the movable said frame members for positively clamping the partially opened tubular wrapper and movable laterally away from each other from an initial clamping position close to the plane of the descending tubular wrapper to a position where said clamping elements will clear the sides of the load on said load-supporting means when said side frames are lowered from said normal raised position to their lowermost position.

2. Load enveloping apparatus as defined in claim 1 wherein means is provided for simultaneously moving the mechanical clamping elements away from each other at substantially the same time and rate.

3. Load enveloping apparatus as defined in claim 1 wherein said sheet gripping means are mounted opposite each other on either side of the descending tubular wrapper and wherein the mechanical clamping elements on one side frame member are opposite those on the other side frame member whereby opposite faces of the flat tubular wrapper can be gripped and initially opened by the sheet gripping means and can be fully opened as said clamping elements move away from each other.

4. Load enveloping and wrapping apparatus as 1 defined in claim 3 wherein there are at least two of said mechanical clamping elements on each side frame positioned to clamp opposite faces of the flattened tube near the side edges thereof to open the tube into a foursided envelope.

5. Load enveloping and wrapping apparatus as defined in claim 1 in which said tubular sheet gripping means and said'clamping elements are carried on the free ends of arcuately movable members pivotally supported on said vertically-movable side frames, said arcuately movable members being movable in an arc from a horizontal position where the gripping means and the clamping elements on opposite side frames most closely approach each other downwardly and outwardly relatively to each other through an arc of about 90.

6. Apparatus as defined in claim 5 in which the gripping means and the clamping elements are rotatably mounted on the outer ends of said arcuately movable members, and means for rotating the gripping means and the clamping elements in a direction opposite the direction of arcuate travel of said arcuately movable members to keep the angular relation of said gripping means and said clamping elements constant in respect to the original vertical plane of said flat tubular sheet as it is fed downwardly into the machine.

7. Apparatus as defined in claim 5 in which there are fluid pressure cylinder and piston units on the side frames arranged to effect the swinging movement of said arcuately movable members.

8. Apparatus as defined in claim 1 in which said side frame members are guided for vertical movement in said upright structural sections of said machine structure.

9. Apparatus as defined in claim 1 in which there is a driving means arranged to move said side frame members vertically in synchronism and isochronism.

10. Apparatus as defined in claim 1 in which said sheet gripping means and said mechanical clamping elements are combined and each comprise:

a. a suction nozzle arranged to draw a portion of the tubular sheet material into it,

b. clamping means associated with said nozzle for gripping and holding the portion of the tubular sheet which is sucked into the nozzle, and

c. means for controllably operating said clamping means to clamp or release the tubular sheet.

11. Apparatus as defined in claim in which said clamping means comprises a movable clamping block mounted in the nozzle and said last-named means comprises a fluid pressure cylinder and piston unit operatively connected with the clamping block.

12. Apparatus as defined in claim 10 in which each side frame member includes a supporting bar extending in the direction of the length of said side frame members, said supporting bars each having a plurality of said combined sheet gripping means and clamping elements thereon.

13. Apparatus for enveloping a load to be packaged with a length of tubular shrink-wrapping material by opening out a flattened tubular wrapper at a level above the load to be wrapped and then pulling it down from above the load around the load, said apparatus comprising:

a. a supporting structure through which a load-conveying and supporting conveyor passes.

vertically movable side frames in said supporting structure extending parallel with the conveyor, one at each side of the conveyor,

0. means for raising and lowering the side frames in unison from a level where they extend above a load positioned on said conveyor to be wrapped to a level extending below the load,

. each side frame having wrapper-vacuum gripping and mechanical clamping means thereon supported for movement on the frame toward and away from the longitudinal central plane of the conveyor, and

e. means for feeding a flattened tubular wrapping strip vertically from the top of said supporting structure down between said vacuum gripping and mechanical clamping means when the side frames are raised and the vacuum gripping and mechanical clamping means of the two side frames are extended to a position nearest said central plane.

14. Apparatus for enveloping a load to be packaged with a shrink-wrapping material comprising:

a. means for feeding a flattened tubular sheet of shrink-wrapping material from an overhead position downwardly toward a load to be wrapped,

. opposed vacuum gripping and mechanical clamping elements supported for simultaneous movement from an uppermost sheet gripping and clamping position in which said elements are in close confronting relation with clearance between them for the downwardly fed flattened tubular sheet downwardly and outwardly to a position of maximum separation and thereby pull said sheet open intov a four-sided tube at a level above the load to be wrapped and further movable downwardly in parallel vertical planes from said position of maximum separation to a lowermost limit of travel,

c. means for controllably effecting such movement of the vacuum gripping and mechanical clamping means,

. load supporting means positioned to hold a load to be wrapped substantially centered under said foursided open tube with the top of the load at a level below said level of maximum separation and the bottom of the load above said lowermost limit of travel of said vacuum gripping and mechanical clamping means, and

e. said vacuum gripping and mechanical clamping means being operable to grip and clamp the faces of the sheet in their uppermost position and operable to release said clamped faces in their lowermost position.

15. Apparatusjas defined in claim 14 wherein said vacuum gripping and mechanical clamping elements each' comprise a suction nozzle for drawing the wrapper sheet into it and movable clamping means selectively operable to mechanically hold the wrapper sheet when it has been drawn into the nozzle and to release it at the required time.

16. Apparatus as defined in claim 14 wherein said opposed vacuum gripping and mechanical clamping elements are mounted at the outer ends of swinging arm structures which are horizontal at said uppermost position of said elements and movable downwardly to said position of maximum separation, and said swinging arm structures are in turn each carried on a vertically movable side frame one of which is at one side of the load-supporting means and one at the other side.

17. Apparatus as defined in claim 16 wherein means is provided for rotating said vacuum gripping and mechanical clamping elements in a vertical arc in a direction opposite the direction in which said swinging arms rotate.

18. Apparatus for enveloping a load carried on a pallet or other base member in a shrink-film wrapping comprising:

a. a machine structure having upright structural sections and cross members connecting the tops of the upright sections and having means positioned within said structure on which a load to be wrapped is supported, 7

b. means on said machine structure for feeding a flat tubular plastic shrinlE film downwardly toward a load positioned on said load-supporting means,

. side frame members movable vertically in said sheet gripping and clamping elements on each of the movable side frame members movable laterally away from each other from a sheet gripping and clamping position close to the plane of the descending tubular wrapper to a position where said sheet gripping and clamping means will clear the sides of the load on said load-supporting means when said side frame members are lowered from said normal raised position to their lowermost position, the said sheet gripping and clamping elements on each movable side frame member each comprising means to first grip a surface of the flattened tubular sheet to initially effect partial opening of the tubular sheet as said elements move away from each other and means which is then operable to mechanically clamp the confronting surface of the partially opened tubular sheet and hold it clamped during the remaining lateral movement of said element and the entire downward travel of the side frame member on which said element is carried, and

sheet gripping and glarnpin g elements. 

1. Apparatus for enveloping a load carried on a pallet or other base member in a shrink-film wrapping comprising: a. a machine structure having upright structural sections and cross members connecting the tops of the upright sections and having means positioned within said structure on which a load to be wrapped is supported, b. means on said machine structure for feeding a flat tubular plastic shrink film downwardly toward a load positioned on said load-supporting means, c. side frame members movable vertically in said machine structure between a normal raised position at a level extending above the top of a load on said load-supporting means to a level extending below the bottom of said load, one of said movable side frame members being movable in a plane at one side of a load on said load-supporting means and the other in a plane at the opposite side, And d. sheet gripping means for gripping and partially opening the lower end of the tubular wrapper and mechanical clamping elements on each of the movable said frame members for positively clamping the partially opened tubular wrapper and movable laterally away from each other from an initial clamping position close to the plane of the descending tubular wrapper to a position where said clamping elements will clear the sides of the load on said load-supporting means when said side frames are lowered from said normal raised position to their lowermost position.
 2. Load enveloping apparatus as defined in claim 1 wherein means is provided for simultaneously moving the mechanical clamping elements away from each other at substantially the same time and rate.
 3. Load enveloping apparatus as defined in claim 1 wherein said sheet gripping means are mounted opposite each other on either side of the descending tubular wrapper and wherein the mechanical clamping elements on one side frame member are opposite those on the other side frame member whereby opposite faces of the flat tubular wrapper can be gripped and initially opened by the sheet gripping means and can be fully opened as said clamping elements move away from each other.
 4. Load enveloping and wrapping apparatus as defined in claim 3 wherein there are at least two of said mechanical clamping elements on each side frame positioned to clamp opposite faces of the flattened tube near the side edges thereof to open the tube into a four-sided envelope.
 5. Load enveloping and wrapping apparatus as defined in claim 1 in which said tubular sheet gripping means and said clamping elements are carried on the free ends of arcuately movable members pivotally supported on said vertically-movable side frames, said arcuately movable members being movable in an arc from a horizontal position where the gripping means and the clamping elements on opposite side frames most closely approach each other downwardly and outwardly relatively to each other through an arc of about 90*.
 6. Apparatus as defined in claim 5 in which the gripping means and the clamping elements are rotatably mounted on the outer ends of said arcuately movable members, and means for rotating the gripping means and the clamping elements in a direction opposite the direction of arcuate travel of said arcuately movable members to keep the angular relation of said gripping means and said clamping elements constant in respect to the original vertical plane of said flat tubular sheet as it is fed downwardly into the machine.
 7. Apparatus as defined in claim 5 in which there are fluid pressure cylinder and piston units on the side frames arranged to effect the swinging movement of said arcuately movable members.
 8. Apparatus as defined in claim 1 in which said side frame members are guided for vertical movement in said upright structural sections of said machine structure.
 9. Apparatus as defined in claim 1 in which there is a driving means arranged to move said side frame members vertically in synchronism and isochronism.
 10. Apparatus as defined in claim 1 in which said sheet gripping means and said mechanical clamping elements are combined and each comprise: a. a suction nozzle arranged to draw a portion of the tubular sheet material into it, b. clamping means associated with said nozzle for gripping and holding the portion of the tubular sheet which is sucked into the nozzle, and c. means for controllably operating said clamping means to clamp or release the tubular sheet.
 11. Apparatus as defined in claim 10 in which said clamping means comprises a movable clamping block mounted in the nozzle and said last-named means comprises a fluid pressure cylinder and piston unit operatively connected with the clamping block.
 12. Apparatus as defined in claim 10 in which each side frame member includes a supporting bar extending in the direction of the length of said side frame members, said supporting bars each having a plurality of Said combined sheet gripping means and clamping elements thereon.
 13. Apparatus for enveloping a load to be packaged with a length of tubular shrink-wrapping material by opening out a flattened tubular wrapper at a level above the load to be wrapped and then pulling it down from above the load around the load, said apparatus comprising: a. a supporting structure through which a load-conveying and supporting conveyor passes. b. vertically movable side frames in said supporting structure extending parallel with the conveyor, one at each side of the conveyor, c. means for raising and lowering the side frames in unison from a level where they extend above a load positioned on said conveyor to be wrapped to a level extending below the load, d. each side frame having wrapper-vacuum gripping and mechanical clamping means thereon supported for movement on the frame toward and away from the longitudinal central plane of the conveyor, and e. means for feeding a flattened tubular wrapping strip vertically from the top of said supporting structure down between said vacuum gripping and mechanical clamping means when the side frames are raised and the vacuum gripping and mechanical clamping means of the two side frames are extended to a position nearest said central plane.
 14. Apparatus for enveloping a load to be packaged with a shrink-wrapping material comprising: a. means for feeding a flattened tubular sheet of shrink-wrapping material from an overhead position downwardly toward a load to be wrapped, b. opposed vacuum gripping and mechanical clamping elements supported for simultaneous movement from an uppermost sheet gripping and clamping position in which said elements are in close confronting relation with clearance between them for the downwardly fed flattened tubular sheet downwardly and outwardly to a position of maximum separation and thereby pull said sheet open into a four-sided tube at a level above the load to be wrapped and further movable downwardly in parallel vertical planes from said position of maximum separation to a lowermost limit of travel, c. means for controllably effecting such movement of the vacuum gripping and mechanical clamping means, d. load supporting means positioned to hold a load to be wrapped substantially centered under said four-sided open tube with the top of the load at a level below said level of maximum separation and the bottom of the load above said lowermost limit of travel of said vacuum gripping and mechanical clamping means, and e. said vacuum gripping and mechanical clamping means being operable to grip and clamp the faces of the sheet in their uppermost position and operable to release said clamped faces in their lowermost position.
 15. Apparatus as defined in claim 14 wherein said vacuum gripping and mechanical clamping elements each comprise a suction nozzle for drawing the wrapper sheet into it and movable clamping means selectively operable to mechanically hold the wrapper sheet when it has been drawn into the nozzle and to release it at the required time.
 16. Apparatus as defined in claim 14 wherein said opposed vacuum gripping and mechanical clamping elements are mounted at the outer ends of swinging arm structures which are horizontal at said uppermost position of said elements and movable downwardly to said position of maximum separation, and said swinging arm structures are in turn each carried on a vertically movable side frame one of which is at one side of the load-supporting means and one at the other side.
 17. Apparatus as defined in claim 16 wherein means is provided for rotating said vacuum gripping and mechanical clamping elements in a vertical arc in a direction opposite the direction in which said swinging arms rotate.
 18. Apparatus for enveloping a load carried on a pallet or other base member in a shrink-film wrapping comprising: a. a machine structure having upright structural sections and cross members connecting the tops of the upright sectiOns and having means positioned within said structure on which a load to be wrapped is supported, b. means on said machine structure for feeding a flat tubular plastic shrink film downwardly toward a load positioned on said load-supporting means, c. side frame members movable vertically in said machine structure between a normal raised position at a level extending above the top of a load on said load-supporting means to a level extending below the bottom of said load, one of said movable side frame members being movable in a plane at one side of a load on said load-supporting means and the other in a plane at the opposite side, and d. sheet gripping and clamping elements on each of the movable side frame members movable laterally away from each other from a sheet gripping and clamping position close to the plane of the descending tubular wrapper to a position where said sheet gripping and clamping means will clear the sides of the load on said load-supporting means when said side frame members are lowered from said normal raised position to their lowermost position, the said sheet gripping and clamping elements on each movable side frame member each comprising means to first grip a surface of the flattened tubular sheet to initially effect partial opening of the tubular sheet as said elements move away from each other and means which is then operable to mechanically clamp the confronting surface of the partially opened tubular sheet and hold it clamped during the remaining lateral movement of said element and the entire downward travel of the side frame member on which said element is carried, and e. means for effecting simultaneous movement of the sheet gripping and clamping elements. 